Photochromic lens

ABSTRACT

A cast photochromic lens including a photochromic film and a cast resin, curable by heat or radiation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/537,571 filed Sep. 29, 2006 now U.S. Pat. No. 7,858,001 entitledPhotochromic Lens, which claims the benefit of priority from U.S.Provisional Application Ser. No. 60/722,848 filed on Sep. 29, 2005entitled Photochromic Lens; and which is a Continuation-In-Part of U.S.application Ser. No. 10/938,275 filed on Sep. 9, 2004 entitledPhotochromic Polyurethane Laminate, which claims the benefit of priorityfrom U.S. Provisional Application Ser. No. 60/501,819 filed Sep. 9, 2003entitled Photochromic Film and Method of Manufacture, and which claimsthe benefit of priority from U.S. Provisional Application Ser. No.60/501,820 filed on Sep. 9, 2003 entitled Photochromic Laminate whichare hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Many methods and devices are known in the art for incorporatingphotochromic characteristics into an ophthalmic lens. One example of amethod known in the art includes imbibing or infusing photochromes intothe host material or base lens from a transfer layer (that issubsequently removed) prior to formation of the finished lens product.Another example of a method known in the art includes incorporatingphotochromes into a lens by imbibing or coating a photochromiccomposition onto the surface of a base lens. Yet another example of amethod known in the art includes incorporating photochromes into afinished lens product by combining a prepared photochromic insert or“laminate” with base lens material, typically via an injection moldingprocess. The following are illustrative examples of such methods knownin the art.

The imbibing process was one of the first processes to be used to impartphotochromicity to plastic lenses. U.S. Pat. No. 4,286,957 to Naour-Senedescribes this process. Further refinements were discussed in U.S. Pat.No. 4,880,667 to Welch. Various improvements to this imbibing processhave been developed, such as described in U.S. Pat. No. 5,130,353 toFisher et. al., and U.S. Pat. No. 5,185,390 to Fisher et. al. These twopatents suggest improvements to the transfer process with a uniquetransfer layer. It was recognized early on that the plastic resins usedto make ophthalmic lenses do not provide the best host material forphotochromes. In such plastic resin materials, the photochromes do notactivate easily and fatigue or wear-out in a short period of time. Astrong activation darkness to near sunglass darkness is desired in themarketplace. Another desired characteristic of a photochromic lens isthat it should maintain at least 70 percent of its original activationdarkness after two years of wear. This is one of the limitations toputting photochromes into polymeric host materials that are used to formthe bulk of the lens.

A more recent example, U.S. Pat. No. 5,728,758 to Smith describes aphotochromic article in which the organic polymeric host material hasbeen impregnated with photochromes prior to formation of the finishedlens product. As is described in the '758 patent, one of the drawbacksof incorporating photochromes directly into the polymeric host materialis the problem of fatigue or light fatigue. Photochromes are believed tolose their ability to change color specifically resulting from theirreversible decomposition of the photochromic compound, which occursdue to repeated exposure to UV light over time. The '758 patentspecifically address this problem by using a unique combination ofmonomers and surface coating compositions to improve abrasionresistance, chemical attack and improved fatigue resistance.

Alternatively, an example that describes coating of a photochromic layeronto the surface of a lens is found in U.S. Pat. No. 4,756,973 toSakagami et al. The '973 patent specifically describes the use ofspirooxazine compound and phenolic compound in the photochromic layer,and describes that such a lens formulation provides successful coloringeffects in photochromic lenses that are subjected to environmentalconditions ranging from normal to high temperatures.

Another example that describes coating photochromes on the surface of alens substrate is found in U.S. Pat. No. 6,150,430 to Walters et al.Specifically, the '430 patent describes a process that includes thesteps of treating the surface of a polymeric substrate to providereactive groups, applying a polymerizable composition to the surface,exposing the coated substrate to radiation to improve adhesion, andapplying and curing a photochromic composition to the coated surface.The '430 patent, at least in part, addresses a method of producingcommercially acceptable “cosmetic” standards for photochromic andnon-photochromic optical coatings that are applied to lenses. A majorlimitation of the photochromic coating approach is the poor scratchresistance of such a coating even with another hard coating on top ofthe photochromic coating. Additionally, if the photochromic coating isscratched, it will result in streaks of areas on the lens that do notactivate.

The limitations of the performance of the photochromes in the variousplastics used to make ophthalmic lenses have resulted in variousimprovement methods, including making composite or multiple part lensesthat combine plastics that are good photochromic hosts with additionalplastics to make improved ophthalmic lenses. One example of thisapproach is described in U.S. Pat. No. 5,531,940 to Gupta et. al.Another approach is to put the photochromic dyes in the glue layerbetween two lens sections as described in U.S. Pat. No. 5,851,328 toKohan. More recent attempts at making photochromic composites aredescribed in U.S. Pat. Nos. 6,863,844 and 6,863,848 to Engardio et. al.and U.S. Publication No. 20050089630 to Schlunt et. al. One problem withthese approaches is that the mechanical stability of the composite isnot very durable in subsequent processing to make the ophthalmic lensand mount it into a frame. Processes such as surfacing the lens toprescription power and edge cutting to fit into a frame result inchipping of the composite due to the different cutting and grindingcharacteristics of the materials. Drilling of the composite to mountinto rimless frames also results in chipping of the composite.

Lastly, the following methods known in the art illustrate incorporationof photochromes into ophthalmic lenses via photochromic inserts orlaminates, whether by cast-mold-type processes or by injection moldingprocesses. For example, U.S. Pat. No. 4,889,413 to Ormsby et al.describes creation of a finished laminate product that is created byplacing two glass or plastic layers into a mold and injecting aphotochromically-infused plastic resin between the glass/plastic layers.The resulting photochromic laminate is thereafter cured and processed,producing a finished lens product.

Another example that illustrates the use of a photochromic insert orlaminate in an injection molding process is described in U.S. Pat. No.6,328,446 to Bhalakia et al. The photochromic laminate or wafer includesinner and outer resin sheets (or protective layers), which sandwich aphotochromic cellulose acetate butyrate layer. The unitary photochromiclaminate is thereafter placed inside a mold cavity, after which a moltenpolycarbonate resin is injected into the cavity and fused to the back ofthe photochromic laminate. The lens is then cooled to room temperatureand the finished product is an injection molded, photochromicpolycarbonate lens.

While each of the above-referenced patents and published applicationsdescribe methods of making photochromic lenses and address particularproblems in the art, improvements are still required. For example,problems associated with impregnating photochromes within the hostmaterial of a base lens have been described to some degree above.Additionally, if such a lens is a semi-finished product and requiresfurther processing (e.g., grinding, polishing, etc), it is clear thatphotochromes present in the base lens will be ground and/or polishedaway, inevitably diminishing the desired coloring effects of thefinished lens product. In addition, the prescription lens must be robustenough to maintain its integrity through subsequent processing to bothform the prescription and be edged, cut and possibly drilled formounting into a frame.

Alternatively, the shortcomings of coating photochromic products ontothe surface of a lens have to do primarily with coating thickness andthe creation of segmented, multi-focal lenses. For example, a coating ofabout 25 μm or more is needed to incorporate a sufficient amount ofphotochromic compounds to provide the desired light blocking quality inthe lens when the compounds are activated. However, a coating of thisthickness is not well suited for application on the surface of asegmented, multi-focal lens because it is too thick. Typically, acoating of this thickness creates such problems as the creation of anunacceptable segment line, as well as coating thickness uniformityissues around the segment line.

Problems that have been raised particularly regarding use ofphotochromic laminates or inserts in injection molding process include,primarily, the bleeding of the functional layer (e.g., photochromiclayer) material of the laminate or wafer. By the term “bleeding,” it ismeant that the functional layer materials between the transparent resinsheets (e.g., the protective layer of the laminate or wafer) runs outfrom between the resin sheets in the lateral direction.

Often bleeding occurs due to the deformation of the photochromic layerunder the high temperature and pressure used during the injectionmolding process. This is thought to occur due to either an excess amountof functional layer material and/or inadequate softening properties ofthe functional layer material. Further, this bleeding can interfere withany additional coating layers that are applied to the lens afterinjection-molding. The Bhalakia patent adequately addresses the issue ofmaking laminates used in injection-molding, through improvement oflaminate materials and properties. However, the issues addressed byBhalakia do not include providing a laminate or insert that may be usedin a cast- lens manufacturing process.

Therefore, a need exists to create a photochromic lens that addressesthe problem of maximizing photochromic properties of a lens produced ina cast-mold manufacturing process.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a photochromic lensthat includes a relatively long service life and provides goodresistance to photochromic dye fatigue. It is another object of thepresent invention to provide a photochromic lens that reduces the amountof photochromic dyes used during the manufacturing process. It is yetanother embodiment of the present invention to provide a photochromiclens that is not limited from use with surface designs, such as bi-focallenses.

It is yet another object of the present invention to provide a method ofmanufacturing a photochromic lens that can utilize most commerciallyavailable cast resins, such as those made by thermoset or radiationinitiated processes. It is yet another embodiment of the presentinvention to provide a photochromic lens having high impact resistance,using known and commercially available high impact resinous layers andmaterials, such as polycarbonate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a photochromic lens according to a preferredembodiment of the present invention.

FIGS. 2A-2D illustrate a photochromic film, as embedded in aphotochromic lens of FIG. 1), according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As seen in FIG. 1, one embodiment according to the present inventionrelates to a photochromic lens comprising a front cast resin layer 1, aphotochromic film 2, and a back cast resin layer 3. Specifically, apreferred embodiment would include a photochromic lens made from a castresin that is either thermoset or radiation-set. The photochromic lensmay be either a finished product or a semi-finished product. In oneembodiment (as shown in FIG. 2), a photochromic lens may include aphotochromic film 2 including at least one protective layer 4 and aphotochromic layer 5 (as shown in FIG. 2, examples (A),(B) and (C)). Inanother embodiment, the photochromic film may include just aphotochromic layer 5 (as shown in FIG. 2, example (D)). In each of theseembodiments, the photochromic film 2 is bonded or adhered strongly to acasting resin layer 1, 3 during a casting process (as shown in FIG. 1).The photochromic film 2 in the form of a laminate may be optimized as ahost for a photochromic dye to provide for maximum performance of thedye.

As seen in FIG. 2, additional embodiments according to the presentinvention would include a photochromic film 2 having at least oneprotective layer 4 and a photochromic layer 5, in a variety oforientations to one another (e.g., FIG. 2, examples (A), (B), and (C)).Not shown are additional hard coating, primer, or barrier coatings thatmay be applied onto the front surface of the protective layer 4 (e.g.,for enhancing adhesion and other performances), the front surfacemeaning the surface of the protective layer 4 facing away from thephotochromic layer 5. When the photochromic layer 5 is used as aphotochromic film 2 without protective layers 4, the photochromic layer5 may also have such hard, primer or barrier coatings applied beforeplacement into the cast lens.

Additional embodiments according to the present invention may include acast photochromic lens including a number of layers and/or combinationsof layers, comprising, for example, protective layers, photochromiclayers or films, and/or additional coating layers (e.g. hard coating,primer layers, and/or other barrier layers)(not shown). Each of theabove-described photochromic lenses can be conveniently manufacturedthrough a casting process.

A suitable photochromic film (laminate) is disclosed in U.S. patentapplication Ser. No. 10/938,275 entitled Photochromic PolyurethaneLaminate, filed Sep. 9, 2004, which is herein incorporated by reference.A preferred material for the protective layers 4 of the photochromicfilm 2 should have good compatibility with the lens casting material. Bythe term “compatibility”, it is meant that the adhesion between theprotective layer 4 and the front cast resin layer 1 formed by the lenscasting material is sufficient to pass ordinary tests for eyewear lenseswithout damage or chemical attack to the protective layers 4 of thephotochromic film 2 (e.g. FDA drop-ball test, drilling and mountingtests).

Examples of preferred materials for the protective layers 4 of thephotochromic film 2 include acrylate resins, cellulose esters, andpolycarbonate resins. Suitable hard coatings known in the art mayfurther protect such protective layer resins to prevent the castingresin from chemically attacking the protective layer resins duringprocessing.

Preferred materials for the photochromic layer 5 of the presentinvention would include, for example, plastic host resins having a glasstransition temperature, T_(g), of less than 50° C., and more preferably,below 30° C. These plastics tend to be mechanically soft which is idealfor the photochromes to activate and de-activate. When the photochromicdyes absorb UV light, typically a carbon-oxygen bond in the photochromicdye molecule is broken and the dye molecule rotates into a form thatabsorbs visible light. A soft plastic host for the dye that wouldfacilitate this action preferably would include a class of plastichosts, such as polyurethanes. However, historically, this mechanicalsoftness of plastic hosts has been shown deficient when such materialsare used as ophthalmic lens materials. Therefore, a preferred embodimentof an ophthalmic lens contemplated for use with the present inventionwould include encapsulation of a host urethane resin, such as aphotochromic layer 5, within an ophthalmic lens. A preferred thicknessof the photochromic layer 5, namely the photochromic urethane layer 5,would preferably be 10 mil or less, more preferably 4 mil or less andmost preferably, to 2 mil or less.

Preferred polyurethane photochromic host materials would include, forexample, thermoplastic and thermoset polyurethanes. Examples of suchhost materials are disclosed in U.S. Pat. Nos. 4,889,413, 6,107,395, and6,166,129, and U.S. patent application Ser. No. 10/938,275, which areherein incorporated by reference. The polyurethane composition wouldpreferably include the following: 0.05% to 6% pbw of photochromiccompound(s), and a stabilizer package: 0.5% to 6% pbw of lightstabilizer(s), 0.5% to 6% pbw of antioxidant(s), 0.5% to 6% pbw of UVabsorber(s). Also, the photochromic film 2 would preferably have athickness no greater than 40 mil.

Any lens casting resins available on the market and known in the artwould be suitable to produce the photochromic lens of the presentinvention. Examples of such casting resins would include CR-39 from PPG(or equivalent from Great Lakes Chemicals denoted by the tradename ofRAV-7) and MR series cast resins from Mitsui. In addition to thermosetresins, cast resins that are curable by radiation energy (e.g., UV) arealso suitable for use with the present invention. The radiation curingprocess is advantageous in that it will not interfere or degrade thephotochromic dyes due to their protection inside the laminate. Examplesof radiation curable cast resins would include, for example, thoseresins based on acrylate chemistry.

It is preferable that the cast resin for the front protective layer 4 ofthe photochromic film 2 should not include UV absorbers, which wouldsignificantly absorb or block the activation wavelength of thephotochromic dye. The photochromic layer 5 of the photochromic film 2would provide adequate UV protection to the eyes, as the photochromicdyes imparted to the photochromic layer 5 are extremely efficientabsorbers of UV.

Examples of manufacturing the photochromic lens as contemplated in thepresent invention would include, for instance, a cast molding process,in which a photochromic film 2 is first placed into a cast mold.Thereafter, a cast resin 1,3 may also be introduced into the cast moldand the lens would be cured, forming an integrate photochromic castlens. The photochromic film 2 may be placed in any number oforientations within the mold, depending upon desired results and lensprocessing applications.

One embodiment for manufacturing the lens of the present invention wouldinclude the steps of preparing a photochromic film 2, as earlierdescribed; forming discs of the film into wafers, preferably having acurve matching the front base curve of the lens to be produced;preparing a cast setup comprising a front mold, a formed wafer, a backlid (mold), in a cast gasket; pouring a cast resin into the front cavityformed by the front mold and the wafer, and the back cavity formed bythe wafer and the back lid (mold); and curing the cast resin to form thephotochromic lens.

Forming of the photochromic film 2 may be done by a variety of differentways familiar to those in the arts. Examples of lens forming techniquesmay include, for instance, compression forming and vacuum forming.

A cast setup used to produce polarizing lenses from cast resins couldalso used to cast the photochromic lens of the present invention withoutany modification.

Another embodiment for manufacturing a lens as contemplated by thepresent invention includes incorporation of photochromes into thepolyurethane plastic, and thus the photochromic film 2, after thepolyurethane has been formed (e.g., after urethane monomers and catalysthave reacted to fully form polyurethane). This is contrary to theteaching of U.S. Pat. No. 4,889,413 (herein incorporated by reference),which describes incorporation of photochromes into the urethanemonomer/catalyst mixture, prior to formation of polyurethane. Further,the teaching of the '413 patent describes a the method of preparing andassembling a lens unlike that of the present invention. The '413 patentdescribes assembly of pre-cast lenses (either plastic or glass), betweenwhich a photochromic host is introduced and thereafter cured.

One embodiment of a method contemplated for use with the presentinvention may include the steps of: dissolving an appropriate amount ofphotochromic dye into a polyurethane resin with an appropriate solvent;casting the resultant solution on a smooth surface, to allow the solventto evaporate; placing the resulting sheet or film of photochromicpolyurethane into a mold with a thermoset casting monomer liquid andcatalyst; and completing a curing or reaction step of the thermosetmonomer into a thermoset, fully cured lens with the polyurethane filmencased inside the thermoset lens.

This particular embodiment would result in a photochromic thermoset,cast lens with improved photochromic properties. Thus, one does not needto mix the photochromes with the polyurethane monomers first. One hasthe option of putting the polyurethane in a laminate as described aboveor not in a laminate inside the lens (plastic host).

EXAMPLE 1

A photochromic film was prepared according to the examples in U.S.patent application Ser. No. 10/938,275. The polyurethane layer is 40 μmthick, and the protective layers are 76 μm cellulose acetate butyrate(CAB) films (K-Mac). The polyurethane layer and protective layers werebonded together to form a photochromic laminate. The laminate was maskedwith a 3M film (24S56W). A 70-mm disk was die-cut off from the abovelaminate, and formed into a 6-base laminate wafer through athermo-vacuum forming process. The temperature was 255° F., and theforming time was 200 seconds. A 70-mm lens cast gasket and two 6-baseglass molds (front and back) were used to cast the photochromic lens.The masked film is thereafter removed prior to placement of the laminatewafer into the gasket. The laminate wafer was fixed in the gasket about1 mm away from the front mold surface with help of a spacer. A clearUV-curable cast resin from OptiCast was injected into the front and backcavities. The front cavity is formed by the front mold and thephotochromic film. The cast resin in the above setup was cured under a12-mW/m² exposure for 10 minutes. The result was a cast resin lenshaving the photochromic film embedded in it. The unactivatedtransmission of the lens was measured as 70%. The activated transmissionafter exposure to a Xenon lamp under 20 W/m² intensity of UV wasmeasured to be 19%. This demonstrated good photochromic activity.

EXAMPLE 2

To a solution of 18% by weight of a polyester urethane (Tecoflex CLC-93Afrom Thermedics) in THF solvent was added 2% each of Tinuvins 765, 144,and Irganox 1010 (all from CIBA Corporation), and 0.8% of naphthopyranphotochromic dye VP0762 (Proprietary Vision-Ease Dye). The mixture wasthen cast on a flat borosilicate glass plate and the solvent allowed toevaporate. A photochromic film of about 0.2 mm thick was obtained. Thephotochromic film was then placed between two glass molds held togetherwith a standard casting gasket. A mixture of 58.3 grams of castingmonomer P11 (NOF Corporation), 0.6 gram of Tinuvin 765, 0.26 gram ofTrigonox 23 catalyst and 0.37 gram of Trigonox 21 catalyst wasintroduced between the glass molds and around the polyurethane film. Themold and gasket assembly was placed in a water bath and cured in a cyclethat ramps the lens up to 90oC over a 20 hour period. The resultantthermoset, cast lens is then separated from the glass molds. The lenshad a refractive index of 1.55. The lens sample was then fatigued byexposure to a Xenon lamp with an ultraviolet light output of 30Watts/Square Meter for 144 hours. This simulates actual wear of the lensby someone for a two year wear period. After the 144 hours, thephotochromic performance remaining was 97%. This compares to theperformance of the commercial photochromic polycarbonate Quantum(Transitions Optical, Inc.) lens product that is believed to be only a65% remaining performance. Thus, the photochromic film in the cast lenswas very fatigue resistant and had longer life than the prior art.

EXAMPLE 3

A photochromic film was prepared according to the examples in U.S.patent application Ser. No. 10/938,275. The polyurethane layer is 40 μmthick, and the protective layers are 350 μm thick polycarbonate films.The polyurethane layer and protective layers were bonded together toform a photochromic laminate. The laminate was masked with a 3M film(24S56W). A 70-mm disk was die-cut off from the above laminate, andformed into a 6-base laminate wafer through a thermo-vacuum formingprocess. The temperature was 255° F., and the forming time was 200seconds. A 70-mm lens cast gasket and two 6-base glass molds (front andback) were used to cast the photochromic lens. The masked film isthereafter removed prior to placement of the laminate wafer into thegasket. The laminate wafer was placed against the front mold surface andplaced into the gasket with the back mold. A clear UV-curable cast resinfrom OptiCast (OPIV-B) was injected into the back cavity. The cast resinin the above setup was cured under a 12-mW/m² UV exposure for 7 minutes.The result was a cast resin lens having the photochromic laminate fusedto the front of it. The unactivated transmission of the lens wasmeasured as 79%. The activated transmission after exposure to a Xenonlamp under 12 W/m² intensity of UV was measured to be 19%. Thisdemonstrated good photochromic activity.

EXAMPLE 4

A photochromic film was prepared by laminating 13.5 mil thick CAB film(Kodacel K7896, made by Eastman Kodak) for both top and bottomprotective layers and 38 micron photochromic layer (polyurethane). Thelaminate was masked with 3M protective masking film (24S56W) on bothsides then a 86 mm disk in diameter was cut-out from the above laminate.It was formed into a 6 base laminate wafer through a thermo-vacuumforming process. The forming temperature was 235° F. and forming timewas 150 seconds. It was further cut to 72.6 mm in diameter to fit thesize of casting mold. It was further cut by 3 mm on two locations toallow flow of the cast resin around it. A 73 mm casting mold and two 6base glass molds were used for front and back to cast a photochromiclens. The masked film is thereafter removed prior to placement of thelaminate wafer into the gasket. Said formed photochromic film was placedin the mold about 1 mm away from the front mold surface with help of aspacer. Thermo-set resin RAV-7 (made by Great Lakes Chemical) without UVabsorbing agent was injected to fill both front cavity and back cavitywhich were separated by the photochromic film. The cast resin in abovesetup was thermally cure in normal condition. The result was a castresin lens having the photochromic laminate fused to the front of it.The unactivated transmission of the lens was measured as 82.4%. Theactivated transmission after exposure to a Xenon lamp under 12 W/m2intensity of UV was measured to be 16%. This demonstrated goodphotochromic activity.

EXAMPLE 5

A photochromic film was prepared by laminating 12 mil thickpolycarbonate film (1151 by Teijin Kasei America) for both top andbottom protective layers and 38 micron photochromic layer(polyurethane). The polycarbonate film was applied with UV curablehardcoat as barrier coating on one side in advance. The hardcoated sidewas placed outside of lamination that later contacts casting resin.Without this barrier coating, this casting resin monomer has been shownto cause the polycarbonate film to turn white and, therefore, usable.The laminate was masked with 3M protective masking film (24S56W) on bothsides then a 86 mm disk in diameter was cut-out from the above laminate.It was formed into a 6 base laminate wafer through a thermo-vacuumforming process. The forming temperature was 285° F. and forming timewas 250 seconds. It was further cut to 72.6 mm in diameter to fit thesize of casting mold. It was further cut by 3 mm on two locations toallow flow of the cast resin around it. A 73 mm casting mold and two 6base glass molds were used for front and back to cast a photochromiclens. The masked film is thereafter removed prior to placement of thelaminate wafer into the gasket. Said formed photochromic film was placedin the mold about 1 mm away from the front mold surface with help of aspacer. Thermo-set resin RAV-7 (made by Great Lakes Chemical) without UVabsorbing agent was injected to fill both front cavity and back cavitywhich were separated by the photochromic film. The cast resin in abovesetup was thermally cure in normal condition. The result was a castresin lens having the photochromic laminate fused to the front of it.The unactivated transmission of the lens was measured as 90.0%. Theactivated transmission after exposure to a Xenon lamp under 12 W/m2intensity of UV was measured to be 19%. This demonstrated goodphotochromic activity.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are proffered by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

1. A cast photochromic lens comprising: a photochromic film interposedbetween two portions of a single cast resin substrate; wherein saidphotochromic film comprises at least one protective layer distinct fromsaid cast resin substrate and a photochromic polyurethane layer, saidphotochromic polyurethane layer prepared from a composition comprising:a solid thermoplastic polyurethane prepared from a compositioncomprising at least one diisocyanate; an isocyanate-terminatedpolyurethane prepolymer; and a photochromic compound; said photochromicpolyurethane layer having a top side and a bottom side, said at leastone protective layer being bonded to at least one side of saidphotochromic polyurethane layer.
 2. The lens of claim 1, wherein saidphotochromic film comprises a thickness of less than 40 mil.
 3. The lensof claim 1, wherein said cast resin substrate comprises a thermosetresin.
 4. The lens of claim 1, wherein said cast resin substratecomprises a radiation-set resin.
 5. The lens of claim 1, wherein said atleast one protective layer comprises a resin selected from a groupconsisting of: acrylate resins, cellulose esters and polycarbonateresins.
 6. A cast photochromic lens comprising: a first cast resin, asecond cast resin; and a photochromic film placed therebetween, saidphotochromic film prepared from a composition comprising: a solidthermoplastic polyurethane prepared from a composition comprising atleast one diisocyanate; an isocyanate-terminated polyurethaneprepolymer; and a photochromic compound; said first cast resin and saidsecond cast resin formed of a same resin.
 7. The lens of claim 6,wherein said photochromic film comprises materials having a glasstransition temperature of less than 50° C.
 8. The lens of claim 6,wherein said photochromic film comprises materials having a glasstransition temperatures of less than 30° C.
 9. The lens of claim 6,wherein said isocyanate-terminated polyurethane prepolymer has amolecular weight of about 1000 to 6000 g/mol.
 10. The lens of claim 6wherein said thermoplastic polyurethane has a molecular weight of about9,000 to 100,000 g/mol.
 11. A cast photochromic lens comprising: aphotochromic film having a first side and a second side, thephotochromic film comprising at least one protective layer and aphotochromic layer; a first cast resin substrate molded to the firstside of the photochromic film; and a second cast resin substrate moldedto the second side of the photochromic film; wherein said first andsecond cast resin substrates are formed of a same resin and wherein theresin is distinct from said at least one protective layer; and whereinsaid photochromic layer is prepared from a composition comprising: asolid thermoplastic polyurethane; an isocyanate-terminated polyurethaneprepolymer; and a photochromic compound.
 12. A lens according to claim11 wherein the photochromic layer comprises a photochromic polyurethane.13. A lens according to claim 11 wherein the photochromic film has athickness of no greater than 40 mil.
 14. A lens according to claim 11wherein said first and second cast resin substrates comprise a thermosetresin.
 15. A lens according to claim 11 wherein said first and secondcast resin substrates comprise a radiation-set resin.
 16. A lensaccording to claim 11 wherein the protective layer comprises a resinselected from a group consisting of: acrylate resins, cellulose estersand polycarbonate resins.
 17. A lens according to claim 11 wherein thephotochromic film comprises a material having a glass transitiontemperature of less than 50 degrees Celsius.
 18. A lens according toclaim 11 wherein the photochromic film comprises a material having aglass transition temperatures of less than 30 degrees Celsius.
 19. Alens according to claim 11 wherein the photochromic layer is interposedbetween two protective layers.
 20. A lens according to claim 11 whereinthe photochromic lens further comprises a layer selected from a groupconsisting of: adhesion layer, polarizing layer, hard-coating layer,primer layer, and barrier layer.